You can cast in casting plaster or fast cast resins. For casting plaster you can use Herculite 2 plaster of tuffcast plaster, all you need to do is mix up your plaster to a creamy consistency, pour in to the mould, level off with a spatula and allow to dry for an hour or more, then simply extract your castings. Repeat to create as many as you like. Now just paint and weather to your liking.